Arrays(1/2D)/ArrayLists

Methods

100

What is the first index of every Array/ArrayList?

0

200

Write the code to change the value of the 3rd element of the following array to 98.

int[] grades = {100, 92, 70, 88, 78}

grades[2] = 98;

300

String[][] letters = {{"A", "B", "C"},
{"D", "E", "F"},
{"G", "H", "I"}};
System.out.println( /* missing code */ );

What code would have the program display "CAGE"?

letters[0][2] + letters[0][0] + letters[2][0] + letters[1][1]

400

Assume that ArrayList nums has the following values: 0, 1, 2, 3, 4

What is printed from the following code:
System.out.println(nums[3] + nums[2] + nums[1]);

Compile Time Error, array required but ArrayList found, wrong types

500

Assume that ArrayList nums has the following values: "z", "o", "tw", "th", "f"

What is printed from the following code:

nums.set(3, "4")

nums.remove(2)

nums.set(1, nums.get(3))

System.out.println(nums);

["f","o","4","f"]

Functions

100

When is a for-each loop not an appropriate traversal method for iterating through an array?

When the goal is to edit the array

When it is not appropriate to look at each element.

200

Write the method/variable that returns the length of each of the following:

String
Array
ArrayList

String: .length()
Array: .length
ArrayList: .size()

300

How do you remove an element from an array? (Not set it blank)

Traverse the old array and add the old elements into a new array with 1 smaller size skipping the element that needed to be removed

400

Assume an ArrayList<Integer> arr has 10 values. Write the code to swap the 3rd and 7th values.

int tmp = arr.set(7, arr.get(2));
arr.set(2, tmp);

500

Write the code or pseudo code to get the last element of a 2D array, arr

arr[arr.length - 1][arr[arr.length - 1].length - 1]

Loops

100

Write the code to create an Array with 10 values. Write a loop to populate the values of the Array with their respective indecies. Print your array with the following code:

System.out.println(Arrays.toString(your array name));

int[] i = new int[10];

for(int x = 0; x < i.length; x++) { i[x] = x; }

Should print [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

200

Write the code for a loop that adds 5 random values from 1-6 into an ArrayList called "diceRolls". Print out those values.

Answers may vary:
ArrayList<Integer> diceRolls = new ArrayList<Integer>();
int c = 5;
while(c-->0) { diceRolls.add((int) (Math.random() * 6) + 1); }

300

What is printed from the following code:

List<String> students = new ArrayList<String>();
students.add("Bob");
students.add("George");
students.add("Edward");
for(String s : students) { System.out.println(s); }

Bob
George
Edward

400

How many values would be updated before the following code errors?
int[][] anArray = new int[8][5];
for (int j = 0; j < 5; j++)
for (int k = 0; k < 8; k++)
  anArray[j][k] = 25;


5

500

for (int num = 0; num < 5; num ++) {
     int tmp = num;
     for (; num < 10; num++) { System.out.println("hop"); }
     num = tmp;
}

How many times will System.out.println("hop") be executed?

40

Vocab

100

Write the code to create an ArrayList of decimal numbers with the name "gpas"

ArrayList<Double> gpas = new ArrayList<Double>();

200

For each of the following write what types of values they can have:

Arrays
2D Arrays
ArrayLists

Array: primitive or objects
2D Arrays: Arrays
ArrayLists: objects

300

What is a for-each (enhanced for loop)? What does it look like?

A for loop with 2 parameters that always loops through all the elements. There is no conditional statement or counter variable.

for(Object o : list) { /* Do Something */ }

400

What is the name of the error you get when trying to access an array element that does not exist?

ArrayIndexOutOfBoundsException

500

How do you change the size of an array? (the answer is not you can't)

Create a new array and assign it to the old variable

Rando cs

100

Write the following for loop as a for each loop!

ArrayList <Integer> a = new ArrayList<Integer>()

biggest = a.get(0);

for (x=1;x < a.size(); x++){

if (biggest < a.get(x)) {biggest = a.get(x)}

}

return biggest

ArrayList <Integer> a = new ArrayList<Integer>()

biggest = a.get(0);

for (Integer element: a){

if (biggest < element) {biggest = element}

}

return biggest

200

String s = "Happy Days";
System.out.println(s.substring(0, 1) + s.substring(2,3) + s.substring(5,6));

Hp_

300

Consider the following code:
for (int num = 0; num < 10; num += 2)  {
}

How many times will num < 10 be checked?

6

400

What is printed from the following code:

String x = new String("20");
String y = new String("20");
System.out.println(x.equals(y));
System.out.println(x == y);

true
false

500

Consider the following code:
int x = (int)(Math.random() * 10) + 20;
int y = (int)(Math.random() * 20) + 10;

What possible values could both x and y share? (Compare the ranges and find the numbers that are the same)

x can be 20-29, y can be 10-29 so they can both be 20-29